1. Field of the Invention
This invention relates to a transmission sensor suitable for measuring turbidity of a fluid. This invention also relates to the use of such a transmission sensor and a method of operation using it.
2. The Prior Art
German Patent Application DE 199 57 592.4 of Nov. 30, 1999 discloses a transmission sensor having a lengthy first measurement zone and a shorter second measurement zone. The two measurement zones are filled with a fluid, the turbidity of which is to be measured during operation of the sensor. The known transmission sensor has a housing with a wall that is transparent for electromagnetic radiation, in particular light, at least in the area of the measurement zones. The transmission sensor has a transmitter, which is arranged in the housing and emits electromagnetic radiation, in particular infrared light, into the measurement zones through an inlet area in the wall. A first receiver of the transmission sensor is situated in the housing and senses the radiation passing through the first measurement zone through a first outlet area in the wall. In a corresponding manner, a second receiver, which is also situated in the housing, senses the radiation transmitted through the second measurement zone through a second outlet area in the wall. The known transmission sensor thus has two independent signal pathways or radiation pathways within the fluid, in particular light pathways, which differ with regard to the path traveled by the radiation between the transmitter and the receiver. By comparing the received signals sensed at the receivers, it is possible to determine the degree of contamination of the fluid, i.e., the turbidity of the fluid.
With the help of such a transmission sensor, a turbidity can be measured in a fluid in particular, where this turbidity develops when the fluid is mixed, i.e., contaminated with solid foreign matter (suspension) and/or liquid foreign matter (emulsion).
Transmission sensors of this type are used, for example, in oil systems that work with hydraulic oils or lubricant oils. For environmental protection reasons, hydraulic oils and lubricant oils should be designed to be environmentally friendly, in particular biodegradable. These requirements result in oils having a comparatively low stability with respect to hydrolytic cleavage when they come in contact with water. In the case of oils, in particular oils that are capable of rapid biological degradation, however, even with traditional mineral oils, a low water content therefore contributes greatly to a long oil lifetime. An unacceptably high water content may lead to aging products, in particular by hydrolysis, and may cause problems with materials and functions in equipment that is supplied with and/or working with such oil. Since water content in oil causes turbidity, in particular in the infrared range, it is possible to monitor the water content in oil by means of such a transmission sensor in order to be able to shut down the respective oil system promptly on reaching a critical water content, for example.
In such an oil system, a so-called “coalescer” may be provided for elimination of water; a coalescer removes water from oil passing through it. Since such a coalescer functions like a fine filter, permanent flow through the coalescer rapidly leads to clogging due to other noncritical impurities entrained by the oil. To prevent such premature clogging of the coalescer, the water content in the oil must be measured with the greatest possible accuracy, so the oil stream passes through the coalescer only when needed.
A transmission sensor of the type defined in the preamble may also be used in a plurality of other applications. For example, with the help of such a transmission sensor, it is possible to monitor the degree of contamination of rinse water in a dishwashing machine or a washing machine, so that fresh water can be added as a function of this degree of contamination. This makes it possible to reduce fresh water consumption. Furthermore, in the food industry, in particular in the beverage industry, such a transmission sensor may be used to monitor the quality of the liquid achieved in production. Likewise, the quality of drinking water and/or wastewater can be monitored by such a transmission sensor. In addition to measuring the turbidity in liquids, the transmission sensor is also suitable for measuring turbidity in gases, e.g., for detection of smoke and/or steam. In particular, such a transmission sensor may be used in a clean room or in an ultraclean room for monitoring the dust content in the air.